1. Field of the Invention
This invention relates to a lighting system, a lighting controller and a lighting control method, by which illumination is periodically varied for realizing a lighting environment comfortable in human terms.
2. Description of the Related Art
A lighting system varying illumination corresponding to aperiodic flicker (for example, having a flickering characteristic of 1/f) or periodic rhythm is conventionally known for realizing a comfortable lighting environment.
Periodic rhythms of human body such as rhythms of breathing, heartbeat, pulsation, brain waves such as xcex1 wave, xcex2 wave, and so on, and the circadian rhythm with respect to the sleep are important factors for maintaining normal condition of human body. Thus, it is considered that the amenity has a strong tie for the rhythms of human body.
Especially, the rhythm of breathing can consciously be controlled on some level. Furthermore, the rhythm of breathing responds to mental situation. When a person feels stress, his breath becomes shallow and the rhythm of breathing becomes faster. Alternatively, when the person feels relaxed with contented mind, his breath becomes deep and the rhythm of breathing becomes slower.
When the breath is shallower, not only the effect of breathing becomes lower, but also the fresh air reaches only to a part of the lungs. As a result, the blood carbon dioxide level becomes higher, and the quantity of oxygen carried to the brain becomes insufficient, so that the person is in a state of tension.
When the breath is deeper, a hormone called Endorphins having sedative action is secreted in human body, so that the person is in a state of relaxation.
Accordingly, it is considered effective to control the rhythm of breathing for making the person be in the state of relaxation.
The inventors have researched the lighting system and the lighting control method for varying the illumination corresponding to a frequency near to the rhythm of breathing so as to realize a comfortable lighting environment (see Publication Gazettes of Japanese Patent Applications H11-96809 and 2000-357591). In our research, the lighting system had been controlled for varying the luminance of the light emitting surface corresponding to a sinusoidal curve. When the research has advanced, it is found that the variation of the luminance of the light emitting surface corresponding to the sinusoidal curve is not the best mode.
Accordingly, it becomes a new problem how the illumination light be varied so as to make the person (the user of the lighting system) fit his breathing rhythm to the variation of the illumination light, and be in the state of relaxation.
Furthermore, the inventors has found that an impression which the person receives from the illumination light becomes different corresponding to the difference of the variation of the illumination light in one period when the person observes the variation of the illumination light, directly. The variation of the luminance of the light emitting surface in one period is defined as a ratio of the highest luminance with respect to the lowest luminance in one period.
The conventional lighting system is designed so that the person observes the variation of the illumination light under opening his eyes. However, the person wishes to feel the relaxation under closing his eyes. When the person closes his eyes, the quantity of the light reaching his pupil is reduced by the eyelids. Since the transmittance of the eyelid is several %, the quantity of the light reaching to the pupil under closing his eyes becomes smaller about several % than the quantity of the light reaching the pupil under opening his eyes.
If the person observes the variation of the illumination light under closing his eyes, the quantity of the light reaching his pupil becomes too small to aware the variation of the illumination light, when the variation of the illumination light by the conventional lighting system is smaller than a predetermined level. Thus, the person cannot adjust the rhythm of breathing, so that he cannot be in the state of relaxation.
Furthermore, it is necessary to be in the state of relaxation while the person sleeps. If the person is not in the state of relaxation in sleeping, he cannot take adequate sleep, and he suffers from insomnia depending on the circumstances. The lighting system varying the illumination light can be used for adjusting the rhythm of breathing of the person so as to sleep easily.
It is natural that the person closes his eyes in sleeping. Furthermore, it is preferable to avoid the dazzling illumination in sleeping, so that necessary to make the illumination light dark as possible.
When the lighting system varying the illumination light is used for adjusting the rhythm of breathing so as to fall asleep, it is required that not only the illumination light can be observed through the eyelids, but also the illumination light be maintained sufficiently dark. It is further necessary to take into consideration of adaptation of darkness of human visual perception. The adaptability of darkness is defined that the sensitivity of human eyes becomes higher so as to aware an object at a dark position where the intensity of the illumination light is smaller. When the person falls asleep, his eyes are generally closed under a very dark circumstance, so that the adaptability of darkness of his eyes fairly advances as time go on. As a result, an intensity of an illumination light which was proper at a certain point becomes dazzling by increasing the sensitivity of visual perception as time go on, so that it becomes a bafflement of falling asleep.
The conventional lighting system used for adjusting the rhythm of breathing for falling asleep has not be considered the above-mentioned adaptation of darkness of human visual perception.
The present invention solves the above-mentioned problems by basing on the results of analysis of the visual characteristics and the breathing exercise of a human body.
A purpose of the present invention is to provide a lighting system, a lighting controller and a lighting control method by which a person can easily adjust the rhythm of breathing corresponding to the variation of the luminance of the light emitting surface so as to be in the state of relaxation.
A lighting system in accordance with an aspect of the present invention comprises a light source and a lighting controller for controlling the light source periodically for varying luminance xe2x80x9cLxe2x80x9d on a light emitting surface of the light source. The lighting controller controls the light source in a manner so that variation of the luminance xe2x80x9cLxe2x80x9d per a unit time in the vicinity at a time tMAX when the luminance xe2x80x9cLxe2x80x9d takes the largest value in one period of the variation of the luminance becomes larger than that in the vicinity at a time tMIN when the luminance xe2x80x9cLxe2x80x9d takes the smallest value.
By such a configuration, it is possible to lead the observer to the state of relaxation without making the observer uncomfortable. Thus, the lighting control system is effective even when the observer does not adjust the rhythm of breathing to the variation of the illumination, purposefully.